Step 1
Preheat the oven to 425 degrees F (220 degrees C). Line 2 jelly roll pans with parchment paper.
Step 2
Beat egg whites in a glass metal or ceramic bowl until soft peaks form. Slowly add white sugar and whip on high speed until the whites are stiff and glossy.
Step 3
Beat almond flour confectioners' sugar eggs and egg yolks in a separate bowl for 3 minutes. Add flour and beat on low speed until combined. Gently fold egg whites into the almond mixture until combined. Divide batter between the jelly roll pans; spread evenly.
Step 4
Bake cake layers in the preheated oven until lightly browned about 5 minutes. Invert onto cooling racks and peel off parchment paper; let cool.
Step 5
Make coffee syrup while cake is cooling. Combine boiling water sugar and coffee powder in a small bowl; stir until dissolved.
Step 6
Stir 2 tablespoons boiling water and coffee powder together for the buttercream. Set aside.
Step 7
Combine sugar 1/4 cup water and vanilla extract in a small saucepan. Bring to a boil. Cook without stirring until an instant-read thermometer inserted into the mixture reaches 255 degrees F (124 degrees C).
Step 8
Meanwhile beat egg and egg yolk in a stand mixer on high speed until pale and foamy. Pour hot sugar syrup carefully down the side of the mixer bowl mixing continuously until the bottom of the bowl feels cool to the touch.
Step 9
Beat butter in a separate bowl until creamy. Add butter gradually to the egg mixture beating until frosting is fluffy. Add the dissolved coffee mixture and beat until well incorporated.
Step 9
Place dark chocolate in a heat-proof bowl. Bring milk and cream to a boil in a saucepan. Pour over chocolate; stir until melted and smooth. Whisk in butter until ganache looks smooth and creamy. Let cool.